How to Fix a Truss Rod That Won’t Move

how-to's, info, thoughts, and musings direct from the Fly-est Parker
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Ken Parker
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How to Fix a Truss Rod That Won’t Move

Post by Ken Parker »

The Problem:
“The truss rod in this particular guitar barely works; there's more relief in this neck than I'm comfortable with.”
For most of our production years, Basswood was the only material used for the necks, and later, we added Mahogany from Central America.

One giant goal was to try to do a “forever” fret job with brutally tough and hard fretwire, which we mostly, eventually kinda pulled off. Very Arrogant became Very Humble.

Is the rod adjusted with an Allen key? That was the early version, and we quickly switched to torx for reliability, as the Allen heads could strip, and weren’t fun to replace. Plus, the way I designed it, there was only room for a weird-shaped little thrust washer, and it was bearing on end grain Basswood, which isn’t superior in compression, to say the least.

On the side of the neck’s stability, though, I can say that very likely whatever it has done by now is likely to stay that way, as a result to the epoxy/glass/carbon skin, they really don’t twist, and no creep at all. The problem with the early ones was that the recipe wasn’t fully developed, and those early shop tolerances were much wider than they came to be later on.

Having said all that, if the neck has too much relief, the way to optimize the rod adjustment it to:
  • Loosen the strings
  • loosen the rod nut
  • apply a drop of oil,
  • clamp or flex the neck backwards over a neck block to induce a giant backbow
  • carefully tighten as much as you dare without making any crushing noises
  • then retune, and see if you’re closer to what you’d hope to expect.
I know, it’s a bit of a mess, but the only other remedy could only be accomplished by angels in heaven. Shame on me. Also, the frets can be dressed, just go slow with sharp files or paper, and don’t get things hot.
”Can the nut be removed and washers added to gain more thread?”
Simple answer, no, it wouldn’t work that way. The rod is .078” music wire with 41-40 (semi tool steel) swaged ends. 

This truss rod was very complicated and expensive to make and install, but had the benefit of weighing 1/6 of a normal ‪3/16‬ inch mild steel truss rod.

I would be surprised if it was out of adjustment range; on those early guitars we used, as it turned out, a LOT more carbon fiber than we needed on the back of the neck. One result of this was that the truss rod had a terrible time shortening the length of the back of the neck because it was way too strong in compression. If that’s the case, I don’t know if there is any real remedy to this, except for removing fret top material.

Over tightening the rod will eventually caused terrible damage at the headstock end of the neck as the washer crushes the basswood and it’s pretty awful.

"It's not me that designed the Fly guitar, it was all of you guys." - Ken Parker
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Re: How to Fix a Truss Rod That Won’t Move

Post by Mr303 »

Thanks Ken
I really enjoy reading technical stuff and that’s a lot of good info.
During “isolation” from foot surgery in March I got caught up on back issues of scientific American so things like this are right up my alley.
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Truss Rod X-Rays

Post by vjmanzo »

I found some old photos of X-Rays of a Fly from the old forum, and thought I’d share them in this related thread for posterity sake:
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